Papers by Yasuyuki Ishikawa
Electrocatalysis, 2015
We have studied the hydrogen oxidation reaction on various catalytic sites at the water/Pt(100) i... more We have studied the hydrogen oxidation reaction on various catalytic sites at the water/Pt(100) interface with first-principles direct molecular dynamics and minimum energy pathway calculations. The calculations indicate that the mechanism for electro-oxidation of H 2 on terrace sites of the Pt(100) surface depends on the concentration of inactive adsorbed hydrogen on the electrode surface. Near the reversible potential, the electro-oxidation follows the Tafel-Volmer homolytic cleavage of H 2 at low coverage of adsorbed hydrogen. If the surface is covered with ca. 1 monolayer of hydrogen, however, the oxidation proceeds by the Heyrovsky-Volmer mechanism. We found good agreement between measured and predicted Tafel plots, indicating that hydrogen oxidation/reduction reaction on Pt(100) takes place via the Heyrovsky-Volmer mechanism under ca. 1 monolayer coverage of inactive adsorbed hydrogen.
Journal of Power Sources, 2012
First-principles calculations are used to analyze the phase stability, formation energy, and Li i... more First-principles calculations are used to analyze the phase stability, formation energy, and Li intercalation potential for a series of layered cathode materials. The calculations show LiNi 0.66 Co 0.17 Mn 0.17 O 2 as a promising cathode for lithium-ion batteries. The layer-structured LiNi 0.66 Co 0.17 Mn 0.17 O 2 is prepared via wet chemical route, followed by annealing at 1123 K and characterized using powder X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The characterization techniques reveal single-phase LiNi 0.66 Co 0.17 Mn 0.17 O 2 with highly ordered structure. Galvanostatic chargeedischarge curves recorded at 1C show the discharge capacity of ca. 167 mAh g À1 and good cyclic performance for 25 cycles.
Journal of Physics: Conference Series, 2007
Theoretica Chimica Acta, 1977
A model potential proposed by Huzinaga and his coworkers has been incorporated into the generaliz... more A model potential proposed by Huzinaga and his coworkers has been incorporated into the generalized coupling operator for open-shell SCF. With this modified operator, valence-only calculations have been performed on the ground and Rydberg excited states of the water molecule and compared with the ab initio SCF results previously reported.
Physical Review A, 1991
The self-consistent-field treatment of the frequency-independent Breit interaction is reviewed wi... more The self-consistent-field treatment of the frequency-independent Breit interaction is reviewed with applications to many-electron atoms. The implementation of the matrix Dirac-Fock-Breit self-consistent-field procedure is presented for Gaussian-type basis sets that show no near-linear dependency problem. The matrix Dirac-Fock-Breit procedure has the advantage over the finitediference approach that it does not complicate the self-consistent-field procedure in basis-set expansion calculations. Basis sets of evenand well-tempered Gaussian functions were used to expand the large and small components of Dirac four-spinors. Expressions are derived for evaluating the matrix elements of the Dirac-Fock-Breit equations. Calculations done on rare-gas atoms He, Ne, Ar, Kr, and Xe and alkaline-earth metals Be, Mg, Ca, and Sr are presented.
Physical Review A, 1996
The relativistic coupled-cluster method is used to calculate ionization potentials and excitation... more The relativistic coupled-cluster method is used to calculate ionization potentials and excitation energies of the barium and radium atoms and their monocations. Large basis sets are used, with l up to 5, the Dirac-Fock or Dirac-Fock-Breit orbitals found, and the external 28 electrons of barium or 42 electrons of radium are correlated by the coupled-cluster method with single and double excitations. Good agreement ͑within a few hundred wave numbers͒ is obtained for the ionization potentials and low excitation energies ͑up to 3 eV for Ba, 4 eV for Ra͒. The Breit interaction has little effect on the excitation energies, but it improves significantly the fine-structure splittings of Ra. Large relativistic effects on the energies are observed, up to 1 eV for barium and 2 eV for radium. The nonrelativistic ground states of Ba ϩ and Ra ϩ are (nϪ1)d 2 D rather than ns 2 S.
Physical Review A, 1995
The relativistic Pock-space coupled-cluster method was applied to the Yb, Lu, and Lr atoms, and t... more The relativistic Pock-space coupled-cluster method was applied to the Yb, Lu, and Lr atoms, and to several of their ions. A large number of transition energies was calculated for these systems. Starting from an all-electron Dirac-Fock or Dirac-Fock-Breit function, many electrons (30-40) were correlated to account for core-valence polarization. High-t virtual orbitals were included (up to t = 5) to describe dynamic correlation. Comparison with experiment (when available) shows agreement within a few hundred wave numbers in most cases. Fine-structure splittings are even more accurate, within 30 cm of experiment. Average errors are at least three times smaller than for previous calculations. Two bound states of Lu are predicted, 6p5d D2 and 6p Po, with binding energies of about 2100 and 750 cm, respectively. The ground state of lawrencium is Pz~z, relativistically stabilized relative to D3f 2, the ground state of Lu. Two states of the Lr anion are bound, 7p Po (by 2500 cm) and 7p6d D2 (by 1300 cm).
Zeitschrift für Naturforschung A, 1981
The construction of the coupling operator given by Adams is examined from the standpoint of SCF c... more The construction of the coupling operator given by Adams is examined from the standpoint of SCF convergeney. A unified, hermitian coupling operator is derived by taking into account optimum mixing for the pairs of occupied orbitals as well as the correct variational conditions
Zeitschrift für Naturforschung A, 1980
A natural orbital multiconfigurational SCF formalism has been applied to the closed shell Hartree... more A natural orbital multiconfigurational SCF formalism has been applied to the closed shell Hartree theory with orthonormal orbitals. A prescription is given for constructing a single, one-electron Hamiltonian with which one can determine all the occupied orbitals. The formalism is suited to the matrix formulation of the orthogonalized Hartree theory for polyatomic systems.
We studied HETGS observations of Capella and LETGS observations of Procyon observed by the Chandr... more We studied HETGS observations of Capella and LETGS observations of Procyon observed by the Chandra X-ray Observatory in order to identify L-shell transitions of M-shell ions of iron, many of which also play an important role in the absorption features associated with spectra from active galactic nuclei. We have recently identified several Fe XVI L-shell transitions in spectra of Capella between 15 and 18Å. With the help of laboratory measurements from the Livermore EBIT-I electron beam ion trap and very accurate calculations, we have now also identified Fe XV lines in the HEG and MEG spectra of Capella. Our analyses of the LETGS spectra of Procyon show that Procyon provides an even better opportunity for studying such iron lines. Procyon is much cooler than Capella and the abundance of lower charge states of iron, i.e., of M-shell iron ions, is much higher. We show that the 15 to 18Å region of the Procyon spectrum contains lines from Fe XVII, Fe XVI, Fe XV, Fe XIV, and, possibly, Fe XIII.
Challenges and Advances in Computational Chemistry and Physics, 2010
World Journal of Nanoscience and Engineering, 2012
We present a scalable, reproducible and economic process for the fabrication of diamond and diamo... more We present a scalable, reproducible and economic process for the fabrication of diamond and diamond-graphene hybrid films using paraffin wax as a seeding source for diamond. The films were characterized using Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Raman spectra show the characteristic band of diamond at 1332 cm −1 and the D, G, and 2D bands of graphene at 1360, 1582 and 2709 cm −1 , respectively. Electron microscopy confirms the microcrystalline nature of the diamond films with crystal size in the range of 0.5 μm to 1.0 μm, and the hybrid film consists of microcrystalline diamond attached to thin, semi-transparent graphene flakes. The graphene-diamond hybrid films exhibit a turn-on field of about 3.6 V/μm with a prolonged current stability of at least 135 h.
The Journal of Physical Chemistry C, 2013
Physical Review Letters, 1994
The low-lying electronic states of element 111 are investigated by the relativistic coupled-clust... more The low-lying electronic states of element 111 are investigated by the relativistic coupled-cluster method based on the Dirac-Coulomb-Breit Hamiltonian. A large basis set (26s21p16d9f7g5h) of Gaussian-type orbitals is used. In contrast to the lighter group 11 elements, the ground state of the atom is 6d 7s' D5/2, the D3/2 state is higher by 2.69 eV, and the 6d' 7s S lies 2.95 eV above the D5/2. The reversal is ascribed to relativistic effects; without them, the S energy is 5.43 eV below the D. The calculated electron affinity of the atom is 1.56 eV, and its ionization potential is 10.6 eV.
Physical Review Letters, 1996
The electron affinity of the rare gas element 118 is calculated by the relativistic coupled clust... more The electron affinity of the rare gas element 118 is calculated by the relativistic coupled cluster method based on the Dirac-Coulomb-Breit Hamiltonian. A large basis set (34s26p20d14f9g6h4i) of Gaussian-type orbitals is used. The external 40 electrons are correlated. Inclusion of both relativity and correlation yields an electron affinity of 0.056 eV, with an estimated error of 0.01 eV. Nonrelativistic or uncorrelated calculations give no electron affinity for the atom. [S0031-9007(96)02040-6]
Physical Review Letters, 1995
The low-lying electronic states of Rf+ and Rf are investigated by the relativistic coupled cluste... more The low-lying electronic states of Rf+ and Rf are investigated by the relativistic coupled cluster method based on the Dirac-Coulomb-Breit Hamiltonian. A large basis set (34s24pl9d13f8g5h4i) of Gaussian-type orbitals is used. The external 36 electrons are correlated. In contrast with recent multiconfiguration Dirac-Fock (MCDF) results, the 7s26d23F2 state is found to be the ground state of the atom, lying about 0.30 eV below the 7s'7p6d'D2 state (the MCDF ground state). The dynamic correlation of the system, requiring virtual orbitals with I up to 6, is responsible for the reversal. The first ionization potentia1 of the atom is predicted at 6.01 eV.
Physical Review B, 2013
The discovery of a high-mobility two-dimensional electron gas (2DEG) in wurtzite ZnO/Zn(Mg)O hete... more The discovery of a high-mobility two-dimensional electron gas (2DEG) in wurtzite ZnO/Zn(Mg)O heterostructures is promising for applications due to the high mobility of the carriers. In this paper, we study the formation and properties of the 2DEG at ZnO/Zn(Mg)O interfaces using first-principles calculations based on hybrid density functional theory. The 2DEG arises from the polarization discontinuity at the interface between the two materials. The uncompensated bound charge at the interface gives rise to an electric field in the bulk of ZnO which confines free carriers close to the interface. We find that the type of the confined carriers is determined by the interface termination, while the amount of charge and the confinement width could be controlled by the Mg doping and the device dimensions.
Physical Review A, 1994
The relativistic Fock-space coupled-cluster method for the direct calculation of ionization poten... more The relativistic Fock-space coupled-cluster method for the direct calculation of ionization potentials and excitation energies (including fine structure) is presented and applied to atomic Au and its ions. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. The CCSD approximation is implemented (where CCSD indicates coupled cluster with single and double excitations), which includes single and double virtual excitations in a self-consistent manner, incorporating therefore the effects of the Coulomb and Breit interactions to all orders in these excitations. A rather large basis set (21s17p lid 7f) of kinetically balanced Gaussian spinors is used to span the atomic orbitals. All calculated energies (ionization potential and electron aifinity of Au, excitation energies of Au and Au+) agree with experiment to 0.1 eV or better, with an average error of 0.06 eV. Fine structure splittings are accurate to better than 0.01 eV.
Physical Review A, 1994
Groundand excited-state energies, as well as ionization potentials and electron affinities, are c... more Groundand excited-state energies, as well as ionization potentials and electron affinities, are calculated for all the alkali-metal atoms Li-Fr by the relativistic Fock-space coupled-cluster method. The coupled-cluster singles and doubles approximation, which includes single and double virtual excitations in a self-consistent manner, is implemented. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. Rather extensive basis sets of balanced Gaussian spinors are used to span the atomic orbitals. The average error for the ionization potentials is 0.09' %%uo and for excitation energies 0.2' %%uo. Electron affinities are less accurate, particularly for the heavier atoms, with errors of 4-9'%%uo for K, Rb, and Cs.
Physical Review A, 1995
The relativistic coupled-cluster method is used to calculate ionization potentials and excitation... more The relativistic coupled-cluster method is used to calculate ionization potentials and excitation energies of Hg and element 112, as well as their monoand dications. Large basis sets are used, with l up to 5, the Dirac-Fock or Dirac-Fock-Breit orbitals found, and the external 34 electrons of each atom are correlated by the coupled-cluster method with single and double excitations. Very good agreement with experiment is obtained for the Hg transition energies, with the exception of the high ()12 eV) excitation energies of the dication. As in the case of element 1 1 1 [Eliav et al. , Phys. Rev. Lett. 73, 3203 (1994)], relativistic stabilization of the 7s orbital leads to the ground state of 112+ being 6d 7s, rather than the d' s ground states of the lighter group 12 elements. The 112 + ion shows very strong mixing of the d s, d s, and d' configurations. The lowest state of the dication is 6d 7s J=4, with a very close (0.05 eV) J=2 state with strong d s and d s mixing. No bound states were found for the anions of the two atoms.
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Papers by Yasuyuki Ishikawa